Wear-resistant aluminum alloy excellent in caulking property and extruded product made thereof

ABSTRACT

A wear-resistant aluminum alloy improved in wear resistance (or viscosity), including: 0.1 to 0.39 wt % of Mg, 3.0 to 6.0 wt % of Si, 0.01 to 0.5 wt % of Cu, 0.01 to 0.5 wt % of Fe, 0.01 to 0.5 wt % of Mn, 0.01 to 0.5 wt % of Cr, and the remainder being Al and unavoidable impurities; and an extruded product using the aluminum alloy.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of International ApplicationNo. PCT/JP02/01885, having an international filing date of Feb. 28,2002, which designated the United States, the entirety of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a wear-resistant aluminum alloyexcellent in caulking properties and an extruded product using the same.

[0003] More particularly, the present invention relates to an aluminumalloy suitably used for automotive brake parts for which wear resistanceto sliding parts and viscosity during plastic deformation such ascaulking are required, and to an extruded product obtained by extrudingthe aluminum alloy.

[0004] As an alloy generally used to secure wear resistance, an alloy inwhich hard Si particles are distributed in aluminum by adding a largeamount of Si, such as a 4032 alloy specified in Japanese IndustrialStandards (JIS) H4140, has been proposed. Japanese Patent ApplicationLaid-open No. 9-176769 discloses an alloy in which extrudability andmachinability are improved while maintaining wear resistance by addingSi, Mg, and Mn.

[0005] However, in the technical field of automotive brake parts and thelike, in which wear resistance in lubricating oil such as brake fluid isnecessary, compressive strength is required in addition to wearresistance. Moreover, viscosity of the material is necessary duringcaulking for assembling the parts.

[0006] A technology of depositing Si dispersion particles in thealuminum alloy by adding a large amount of Si, as described above, inorder to improve wear resistance is known in the art.

[0007] However, viscosity of the metal material is decreased bydispersing Si particles in the alloy due to its notch effect.

[0008] Moreover, extrusion formability is decreased.

[0009] Therefore, not only extrusion productivity, but also viscosity isdecreased in the aluminum alloy obtained by merely increasing the amountof Si added. Therefore, it is difficult to apply such an aluminum alloyto parts obtained by machining an extruded product of such an aluminumalloy and assembled with sliding parts such as a piston or valve, sincesuch parts are relatively subjected to sliding wear and required to havecompressive performance against lubricating oil sealed therein.

BRIEF SUMMARY OF THE INVENTION

[0010] According to one aspect of the present invention, there isprovided a wear-resistant aluminum alloy excelling in caulkingproperties, comprising 0.1 to 0.39 wt % of Mg, 3.0 to 6.0 wt % of Si,0.01 to 0.5 wt % of Cu, 0.01 to 0.5 wt % of Fe, 0.01 to 0.5 wt % of Mn,0.01 to 0.5 wt % of Cr, and the remainder being Al and unavoidableimpurities.

[0011] According to another aspect of the present invention, there isprovided a wear-resistant aluminum extruded product excelling incaulking properties, comprising 0.1 to 0.39 wt % of Mg, 3.0 to 6.0 wt %of Si, 0.01 to 0.5 wt % of Cu, 0.01 to 0.5 wt % of Fe, 0.01 to 0.5 wt %of Mn, 0.01 to 0.5 wt % of Cr, and the remainder being Al andunavoidable impurities.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0012]FIG. 1 (Table 1) is a table showing components of aluminum alloysaccording to the present invention.

[0013]FIG. 2 (Table 2) is a table showing extrusion conditions and heattreatment conditions for aluminum alloys according to the presentinvention.

[0014]FIG. 3 (Table 3) is a table showing evaluation results of anextruded product obtained by the present invention.

[0015]FIG. 4 (Table 4) is a table showing multiple regression analysisresults.

[0016]FIG. 5 shows a cross-sectional shape of an extruded productsubjected to evaluation.

[0017]FIG. 6 is a schematic diagram for illustrating a method of testingthe critical upsetting ratio. An upper mold is denoted by 1, and a lowermold is denoted by 3. A test specimen 2 is inserted between the uppermold 1 and the lower mold 3 to be compressed.

[0018]FIG. 7 shows an example in which a hollow 6 of an assembling part5 is utilized to caulk an ABS body material 4 to the assembling part 5by a punch 7.

[0019]FIG. 8 shows an example in which an offset section 61 of anassembling part 51 is utilized to caulk an ABS body material 4 to theassembling parts 51 by a punch 71.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0020] Conventionally, viscosity and caulking properties of the aluminumalloy are decreased by improving wear resistance, and wear resistanceand strength are decreased by improving caulking properties. Therefore,these properties are considered to be conflict with each other.

[0021] An extruded product as shown in FIG. 5 was formed by addingvarious components to an aluminum metal and extruding the aluminumalloy. Quality characteristics, extrudability, hardness, mechanicalproperties, and compressibility were evaluated by experiment.

[0022] As the first step, a wear resistance test was conducted in orderto determine the amount of Si to be added for securing wear resistancenecessary for an anti-lock braking system actuator body (hereinaftercalled “ABS body”) which is an automotive brake part.

[0023] A wear resistance effect was recognized by adding 3.0 wt % of Si(“%” used hereinafter indicates “wt %”). The wear resistance effect wasnot further improved when adding Si in an amount of 6.0% or more.Therefore, the amount of Si to be added is suitably 3.0 to 6.0%, andpreferably 3.5 to 5.5%.

[0024] If the amount of Si added is too great, extrudability isdecreased. Therefore, the amount of Si to be added is ideally 3.5 to5.0% taking extrudability into consideration.

[0025] The wear resistance was evaluated by relative comparison ofresults obtained under the following conditions.

[0026] A friction and wear tester (“EFM-III-F” manufactured by OrientecCo., Ltd.) was used.

[0027] As the test method, two cylindrical specimens (pin and specimendisk) are rotated along the center line, and friction and wear arecaused to occur by pressing the pin against the disk while applying aconstant load.

[0028] The pin was an SCr20 (carburized and quenched) material with adiameter of 5 mm and a height of 8 mm.

[0029] The specimen disk was cut from a T6-treated (T6 tempered)extruded material, and processed to have a diameter of 60 mm, height of5 mm, surface roughness of 1.6 Z or less, and flatness of 0.01.

[0030] Brake fluid was used as lubricant. The rotational speed was 160rpm, the test period was 50 hours, and the load was 20 MPa.

[0031] The amount of wear was measured by measuring the worn part of thespecimen disk using a roughness measuring instrument.

[0032] Since strength cannot be secured by adding only Si, Mg is addedin order to improve strength due to the precipitation effect of Mg₂Si.For example, the ABS body material must have hardness (evaluated bysurface hardness) HRB (Rockwell B scale) of 35 or more, tensile strengthof 240 MPa or more, and 0.2% yield strength of 190 MPa or more.

[0033] If the amount of Mg added is 0.6% or more, although strength canbe secured, viscosity of the material is decreased. As a result, in thecase of using such a material as the ABS body material, it is difficultto form a hole for allowing insertion of sliding parts such as a pistonor valve and to perform caulking such as ball caulking. In the worstcase, cracks occur in the ABS body material during caulking.

[0034] Caulking is described below.

[0035] An example shown in FIG. 7 illustrates a processing method inwhich an assembling part 5 provided with an assembling hollow 6 issecured to an ABS body material 4 using a jig or the like, and the metalof the ABS body material is caused to flow into the hollow 6 by pressingthe ABS body material 4 from the side using a punch 7, whereby the ABSbody material 4 is assembled on the assembling part 5.

[0036] A stroke L1 of the punch 7 is the caulking depth.

[0037] In an example shown in FIG. 8, an assembling part 51 providedwith an offset section 61 is secured to the ABS body material 4 using ajig or the like, and the metal is caused to flow into the offset section61 by pressing the ABS body material 4 from the side using a punch 71,whereby the ABS body material 4 is assembled on the assembling part 51.

[0038] A stroke L2 of the punch 71 is the caulking depth.

[0039] As the evaluation method for caulking properties, a test specimen2 was placed between an upper mold 1 and a lower mold 3 as shown in FIG.6, and a critical upsetting ratio at which microcracks occur in the testspecimen when pressure is applied to the test specimen from the top wasevaluated as compressibility. The component which influences qualitycharacteristics was extracted by multiple regression analysis.

[0040] The results are shown in FIG. 4 (Table 4).

[0041] As is clear from these results, it was found that Mg and Mn havea considerable influence on the critical upsetting ratio. Therefore, theamount of these elements was examined while taking tensile strength andsurface hardness into consideration.

[0042] A material to which Mg was added in an amount of 0.6% or more hada critical upsetting ratio, at which microcracks occur, of 40%. Amaterial to which Mg was added in an amount of 0.5% had a criticalupsetting ratio of 42%. A material to which Mg was added in an amount of0.2% had a critical upsetting ratio of 50% or more.

[0043] The amount of Mg added has a negative correlation with thecritical upsetting ratio. Therefore, in order to secure strength andcaulking properties necessary for the ABS body material, the amount ofMg to be added is 0.1 to 0.45%, and preferably 0.2 to 0.45%.

[0044] Mn has a grain refinement effect. However, the amount of Mn addedhas a negative correlation with the critical upsetting ratio. Therefore,the amount of Mn to be added is suitably 0.01 to 0.5%, and preferably0.01 to 0.3%.

[0045] Cu contributes to a solid-solution effect in aluminum andimproves hardness. However, corrosion resistance is decreased if theamount of Cu added is too great. Therefore, Cu is suitably added in anamount of 0.01 to 0.5%.

[0046] Cr, Fe, and Ti have a grain refinement effect. These elements arearbitrarily added.

[0047] The practical ranges for Cr, Fe, and Ti are respectively 0.01 to0.5%, 0.01 to 0.5%, and 0.01 to 0.2%.

[0048] An eight-inch billet having an alloy composition shown in FIG. 1(Table 1) was cast. As shown in FIG. 2 (Table 2), the billet wassubjected to a homogenization treatment at 460 to 590° C. for six hoursor more, and hot-extruded at 450 to 510° C.

[0049] As a T6 treatment, the hot-extruded product was quenched at thedie end immediately after extrusion, and subjected to an artificialaging treatment by performing a heat treatment at 160 to 195° C. for 2to 8 hours.

[0050] The extruded product was formed into the shape shown in FIG. 5.Extrudability of the resulting extruded product was evaluated.

[0051] The extruded product after artificial aging was cut to 90 mm.Hardness, mechanical properties, and compressibility as substitutionevaluation for caulking properties were evaluated according to thefollowing test methods.

[0052] (1) The maximum extrusion rate at which the product can beextruded without causing cracks to occur on the surface of thehot-extruded product was measured. Extrudability of each alloy wasevaluated according to the maximum extrusion rate.

[0053] (2) The surface hardness of the T6-treated extruded product wasevaluated using a Rockwell B scale hardness tester.

[0054] (3) A tensile test specimen specified in JIS 13B was collectedfrom the T6-treated extruded product, and tested according to JIS Z2241.

[0055] (4) Compressibility was evaluated using a cold upsettability testmethod.

[0056] The end restraint upsetting test of a cylindrical test specimenwas conducted.

[0057] A test specimen with a diameter of 14 mm and a height of 21 mmwas collected from the T6-treated extruded product in the extrusiondirection. The test specimen was subjected to cold upsetting pressing inthe axial direction, and the critical upsetting ratio at whichmicrocracks occurred on the side surface was calculated.

[0058] The critical upsetting ratio was calculated according to thefollowing equation.

εhc=(h0−hc)/h0×100

[0059] εhc indicates the critical upsetting ratio (%), h0 indicates theoriginal height of the test specimen, and hc indicates the height of thetest specimen when cracks occurred.

[0060] The test was conducted at room temperature and a compressionspeed of 10 mm/s. An autograph (25 t) was used as the test instrument.

[0061] The evaluation results obtained by the above method are shown inFIG. 3 (Table 3).

[0062] As a result, as opposed to a conventional wear-resistant alloy Jevaluated as a comparative example, a novel aluminum alloy exhibitingwear resistance and compressibility (caulking properties) whileimproving extrudability and its extruded product can be obtained bysetting the Mg content at 0.1 to 0.45 wt %, the Cu content at 0.01 to0.5 wt % and preferably 0.01 to 0.2 wt %, the Si content at 3.0 to 6.0wt %, and the Mn content at 0.01 to 0.5 wt % and preferably 0.01 to 0.3wt %.

[0063] The aluminum alloy according to the present invention excels inextrudability in comparison with a conventional wear-resistant alloy.The extruded product obtained by using the aluminum alloy exhibits wearresistance, strength, hardness, and caulking properties (or viscosity),which have been considered to conflict with these properties. Therefore,the aluminum alloy and the extruded product can be used as an aluminumalloy and an extruded product used for products for which wearresistance, compressive strength, and caulking properties duringproduction working are required.

What is claimed is:
 1. A wear-resistant aluminum alloy excelling incaulking properties, comprising 0.1 to 0.39 wt % of Mg, 3.0 to 6.0 wt %of Si, 0.01 to 0.5 wt % of Cu, 0.01 to 0.5 wt % of Fe, 0.01 to 0.5 wt %of Mn, 0.01 to 0.5 wt % of Cr, and the remainder being Al andunavoidable impurities.
 2. A wear-resistant aluminum extruded productexcelling in caulking properties, comprising 0.1 to 0.39 wt % of Mg, 3.0to 6.0 wt % of Si, 0.01 to 0.5 wt % of Cu, 0.01 to 0.5 wt % of Fe, 0.01to 0.5 wt % of Mn, 0.01 to 0.5 wt % of Cr, and the remainder being Aland unavoidable impurities.